Research is continuing in the area of pathophysiology and genetic determinants of congenital adrenal hyperplasia and related conditions. Radioimmunoassay of steroid metabolites in serum specimens is used to probe disorders responsible for virilization of female and undervirilization of male infants; regulation of therapy in adrenal hyperplasia; decline in activity of the fetal zone of the adrenal cortex after birth; increase in androgenic steroid production at adrenarche; gonadal function in pubertal males and females with deficiency of 3-beta hydroxysteroid dehydrogenase; and variability of expression of the 21-hydroxylase enzyme defect in obligatory heterozygote carriers. We propose a population study of HLA haplotypes in the adrenal hyperplasia families, with particular emphasis upon a possible relationship of HLA to expression of metabolic abnormalities in heterozygotes.